/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.socket.sockjs.transport.handler;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.regex.Pattern;

import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.lang.Nullable;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StringUtils;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.sockjs.SockJsException;
import org.springframework.web.socket.sockjs.frame.SockJsFrame;
import org.springframework.web.socket.sockjs.frame.SockJsFrameFormat;
import org.springframework.web.socket.sockjs.transport.SockJsSession;
import org.springframework.web.socket.sockjs.transport.SockJsSessionFactory;
import org.springframework.web.socket.sockjs.transport.session.AbstractHttpSockJsSession;
import org.springframework.web.util.UriComponentsBuilder;
import org.springframework.web.util.UriUtils;

/**
 * Base class for HTTP transport handlers that push messages to connected clients.
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 */
public abstract class AbstractHttpSendingTransportHandler extends AbstractTransportHandler
        implements SockJsSessionFactory {

    /**
     * Pattern for validating callback parameter values.
     */
    private static final Pattern CALLBACK_PARAM_PATTERN = Pattern.compile("[0-9A-Za-z_\\.]*");


    @Override
    public final void handleRequest(ServerHttpRequest request, ServerHttpResponse response,
                                    WebSocketHandler wsHandler, SockJsSession wsSession) throws SockJsException {

        AbstractHttpSockJsSession sockJsSession = (AbstractHttpSockJsSession) wsSession;

        // https://github.com/sockjs/sockjs-client/issues/130
        // sockJsSession.setAcceptedProtocol(protocol);

        // Set content type before writing
        response.getHeaders().setContentType(getContentType());

        handleRequestInternal(request, response, sockJsSession);
    }

    protected void handleRequestInternal(ServerHttpRequest request, ServerHttpResponse response,
                                         AbstractHttpSockJsSession sockJsSession) throws SockJsException {

        if (sockJsSession.isNew()) {
            if (logger.isDebugEnabled()) {
                logger.debug(request.getMethod() + " " + request.getURI());
            }
            sockJsSession.handleInitialRequest(request, response, getFrameFormat(request));
        } else if (sockJsSession.isClosed()) {
            if (logger.isDebugEnabled()) {
                logger.debug("Connection already closed (but not removed yet) for " + sockJsSession);
            }
            SockJsFrame frame = SockJsFrame.closeFrameGoAway();
            try {
                response.getBody().write(frame.getContentBytes());
            } catch (IOException ex) {
                throw new SockJsException("Failed to send " + frame, sockJsSession.getId(), ex);
            }
        } else if (!sockJsSession.isActive()) {
            if (logger.isTraceEnabled()) {
                logger.trace("Starting " + getTransportType() + " async request.");
            }
            sockJsSession.handleSuccessiveRequest(request, response, getFrameFormat(request));
        } else {
            if (logger.isDebugEnabled()) {
                logger.debug("Another " + getTransportType() + " connection still open for " + sockJsSession);
            }
            String formattedFrame = getFrameFormat(request).format(SockJsFrame.closeFrameAnotherConnectionOpen());
            try {
                response.getBody().write(formattedFrame.getBytes(SockJsFrame.CHARSET));
            } catch (IOException ex) {
                throw new SockJsException("Failed to send " + formattedFrame, sockJsSession.getId(), ex);
            }
        }
    }


    protected abstract MediaType getContentType();

    protected abstract SockJsFrameFormat getFrameFormat(ServerHttpRequest request);


    @Nullable
    protected final String getCallbackParam(ServerHttpRequest request) {
        String query = request.getURI().getQuery();
        MultiValueMap<String, String> params = UriComponentsBuilder.newInstance().query(query).build().getQueryParams();
        String value = params.getFirst("c");
        if (StringUtils.isEmpty(value)) {
            return null;
        }
        String result = UriUtils.decode(value, StandardCharsets.UTF_8);
        return (CALLBACK_PARAM_PATTERN.matcher(result).matches() ? result : null);
    }

}
